Why is a girl scared of getting attached?

I met a girl recently who is both physically attractive and has a great personality. We are so similar in how we act and think that it is almost eerie. She is getting over a bad breakup and mentioned that she didn't want a relationship from the start.

However, we hung out few times and found we have so many things in common and she even mentioned to me that she usually doesn't open up to people but it is different for me. We had relations a few times and it was great. Then one day out of the blue she mentioned that she is not ready for anything right now and scared of getting attached. She also told me that affection makes her feel uncomfortable because she is not used to it. So I backed off from showing affection and then she confuses me because the few times we are alone together, she would show me affection by holding my hand or kissing me. I feel that her fear is taking over her emotions and she is now slowly trying to push me away. What do you make of the situation?
Why is a girl scared of getting attached?
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